All publications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Suspension systems for vehicles are well known and comprise a means for attachment of the wheels to the vehicle frame or body and include springs, leafs and/or dampers. The arrangement allows for substantially vertical travel of the wheels while keeping the tire in contact with the ground, thus ensuring maximum tire contact, leading to greater grip and control of the vehicle. Various methods and devices have been used to allow independent movement of each wheel in the vertical plane while retaining maximum tire contact with the road when negotiating bumps and corners. Suspension systems have also evolved to maintain better control of displacement around the vertical and horizontal axis, which might adversely affect the handling of a vehicle. A combination of struts, e.g. Macpherson, lower links, torsion bars, double wishbones, radial arms, trailing arms and beam axles are typical well known examples of such suspension systems.
The most prevalent of these well known suspension designs used in four-wheeled vehicles are the “solid beam” or “live axle” paired with transverse leaf springs. These solid beam/live axle designs are attached to longitudinally mounted leaf springs and coil springs. These crude, yet economic, suspension designs are still in use today, primarily in four-wheeled utility vehicles and trucks. Solid beam/live axle designs, regardless of how they are sprung, suffer from several major shortcomings. Amongst these shortcomings are “bump steer,” high “unsprung mass” and poor packaging, as they occupy a considerable amount of space in the vehicle chassis. While solid beam/live axle designs have relatively no wheel scrub and can achieve high levels of wheel travel, they are “dependent” designs, where one side of the suspension cannot help but alter camber on the wheel/tire on the opposite side of the suspension when encountering undulations in the road/ground surface. This dependence results in “bump steer” and causes a change in the vector of the wheels/tires. This is especially problematic in live axle front suspensions when cornering. Bump steer alters the course of the vehicle in an unsafe manner. In addition, the high unsprung mass of live axles results in a rough ride and a slow-reacting suspension. The poor packaging characteristics of live axles require that large amounts of room in the chassis be allocated for suspension articulation.
The major shortcomings in solid beam/live axle suspension designs led to the advent of the “independent” suspension system. Although independent suspensions were a major improvement over solid beam/live axle suspension designs, independent suspensions also have notable shortcomings related to tire scrub, and camber and toe change all relating to the fact that the tire and wheel assembly move in an arc as they articulate.
Independent suspension designs began with swing axles and sliding pillar suspension designs and later moved on to more advanced designs including the Macpherson/Chapman struts, upper and lower A-arm suspension designs (a.k.a. short-long arm or double wishbone designs) and multi-link suspension designs. Unfortunately, all of these independent suspension designs suffer from wheel scrub and some degree of camber change throughout the wheel's articulation, as well as toe changes leading to variations in under-steer and over-steer. Because current independent designs cause a wheel to travel in an arc, the vehicle cannot have a static track-width. The lack of a static track-width causes problems with bump-steer and vehicle stability. Independent suspension designs also have limited amounts of wheel travel making them a poor choice for vehicles that require a high degree of wheel travel (e.g., off-road and military vehicles).
Early swing axle suspension designs suffered from high degrees of wheel scrub and camber change. Wheel scrub results in high levels of tire wear and negatively affects handling characteristics and camber change resulted. It may also cause unpredictable handling and severe over-steer or under-steer, depending on steering placement. Sliding pillar designs suffer from high levels of friction, thus resulting in high tire wear, increased tire heat, poor rebound performance and a relatively rough ride.
Later came the Macpherson/Chapman Strut designs which represented a seminal design change in independent suspensions, and worked relatively well and had good packaging. Wheel scrub and bump-steer remained unresolved problems with the Macpherson/Chapman strut design as did issues with camber change and limited wheel/tire travel. Upper and lower A-arm (double wishbone) suspensions feature very limited camber change when designed for short wheel/tire travel (but not in long wheel/tire travel designs) and suffer from severe wheel scrub and track change. In addition, all variants of existing suspension systems also exhibit steering geometry variations contributing to over steer and under steer.
The most recent development in suspension systems are the multi-link designs that have improved upon previous suspension systems by reducing unsprung mass and limiting camber change when designed for short travel applications. However, like other independent suspension designs, multi-link designs suffer from wheel/tire scrub, bump steer, undesirable chamber change and also have inherently low potential for large amounts of wheel travel.
All variants of existing suspension systems exhibit steering geometry variations as a result of wheel scrub/track-change. This contributes to over-steer or under-steer depending on the use of either leading or trailing steering arms. Bump-steer occurs when the wheel travels on a different arc than the steering tie-rod. When the steering is pointed straight ahead the wheel and tie-rod are on the same arc of motion. However this is no longer true when turning through a corner where the tie rod and its arc of motion have moved in or out with relation to the arc of the wheel/tire.
The increased level in performance of modern vehicles and tires has magnified the shortcomings of existing suspension systems, and in certain applications, has become the major hurdle in achieving better performance. For example, in off-road racing applications, the high degree of travel in the suspension system leads to various changes in suspension geometry, in turn leading to changes in track width, camber, castor, and toe. These variations limit the degree of certainty engineers may rely upon in developing suspension systems for better traction and performance. In the most popular Macpherson/Chapman strut applications, as the wheel and tire combination at the front of a four-wheeled vehicle rebounds, load is relieved on the particular wheel/tire and the wheel/tire geometry travels towards positive camber. The wheel also travels in an arc, increasing tire scrub and depending on the steering mechanism, leading to either over-steer or under-steer. As load is reestablished on the wheel/tire combination and the suspension system is compressed, the suspension geometry forces the wheel/tire to change from positive camber to neutral and then to negative camber. The arc of motion once again leads to large degrees of tire scrub and alters steering geometry by increasing and/or decreasing under-steer or over-steer. Accordingly, articulation of the suspension system leads to variations in the contact patch and directional vector of the tire/wheel, creating havoc for the driver trying to keep the vehicle in control.
As one can ascertain, there exist substantial advantages in establishing a vehicle's camber, tire scrub and/or toe whilst also eliminating track-change and bump-steer. There further exist advantages in providing a suspension system capable of controlling and varying camber change according to pre-determined settings. Further advantages are gained by providing a method for controlling articulation of a suspension system capable of setting desired rates for camber, castor, tire scrub, and toe such that the desired rates remain consistent throughout the articulation realm of the suspension system.
The present invention describes v-arm and x-arm suspension designs and methods of use thereof that resolve existing impediments in suspension geometry. The v-arm and x-arm suspension designs may be adapted to provide various amounts of wheel travel, while offering fully independent operation, relatively low unsprung mass and compact packaging. The v-arm and x-arm suspension designs overcome the shortcomings of prior independent suspension designs by completely eliminating wheel scrub, bump steer and camber change. Also, unlike other independent designs, large amounts of wheel travel can be incorporated into the design if desired, while maintaining a very compact overall package.